. Comparative anatomy. Anatomy, Comparative. 444 COMPARATIVE ANATOMY External Genitals. The external genitals of the two sexes, like the gonads, have similar beginnings. Slight differences, however, quickly make their appearance. In an 8 mm. embryo, a rounded eminence, the genital tubercle, develops between the tail and the umbilical cord. Along its caudal surface extends a shallow urethral groove bordered by urethral. A B Fig. 371.—Development of the male external genitalia of man. A, indififerent stage from which either sex may develop; B, early, and C, later stages; a, anus;/, genital folds
. Comparative anatomy. Anatomy, Comparative. 444 COMPARATIVE ANATOMY External Genitals. The external genitals of the two sexes, like the gonads, have similar beginnings. Slight differences, however, quickly make their appearance. In an 8 mm. embryo, a rounded eminence, the genital tubercle, develops between the tail and the umbilical cord. Along its caudal surface extends a shallow urethral groove bordered by urethral. A B Fig. 371.—Development of the male external genitalia of man. A, indififerent stage from which either sex may develop; B, early, and C, later stages; a, anus;/, genital folds; g, urogenital groove; p, genital prominence; r, genital ridge (outer genital folds); s, scrotum. (From Kingsley's " Comparative Anatomy of Vertebrates," after O. Hertwig.) folds, the inner genital folds. Labial or scrotal swellings, the outer genital folds, border the urethral folds laterally. When the embryo has reached a length of 15 mm., the urethral groove is perceptibly longer in the male. In both sexes the tubercle elongates to form a phallus, the termination of which enlarges as the glans penis or the glans clitoridis. PERITONEUM PERlTONaJM. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : P. Blakiston's Son
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